How to Repair a Leaking Metal Gas Tank Without Welding

Video tutorial on how to repair a leaking metal fuel tank without welding. I haven’t tried this method on a plastic fuel tank, but this procedure can possible be used on that as well. Unfortunately on my 1984 BMW 733i I am experiencing a fuel tank when the tank is full. At first I expected this to be a faulty rubber line, but unfortunately that wasn’t the case after it was removed.

Tools/Supplies Needed:

• tank sealant (PR-1422 CLASS B FUEL TANK SEALANT SEMKIT - B2)
• grinder
• primer (etching and filler)
• sandpaper
• sandblaster
• rust converter
• paint
• degreaser
• polyurethane film
• foam vibration pads

• tank sealant (PR-1422 CLASS B FUEL TANK SEALANT SEMKIT - B2)
• grinder
• primer (etching and filler)
• sandpaper
• sandblaster
• rust converter
• paint
• degreaser
• polyurethane film
• foam vibration pads

Removal procedures will vary between vehicles, I will have a video covering the specific removal for this car which will be released in the future. A new oem tank is over $700 Canadian and finding a used tank is next to impossible locally. Not to mention a used tank may not be in very good condition either. While this is a metal tank, it can be welded. However, it’s not something I’d recommend as there is a high risk of the tank exploded and I don’t know anyone locally who offers such a service.

As a rough overview for the removal of this car, there is a panel in the trunk where I can gain access to the fuel pump, this is where I can disconnect the fuel lines and electrical connections for the pump and sending unit. The battery has already been disconnected on the car. I have ran the car low on fuel so the tank won’t be as heavy so it’s more manageable to deal with during the removal process. Any covers around the tank were removed.

Place the jack under the tank, usually it’s best to have a piece of wood, something which makes the jack pad wider so you don’t damage the tank. Remove the bolts for the straps and they will typically swing down as they clip in on the opposite side.

I also removed the rubber cover in the gas cap area, along with the gas cap so it didn’t catch up on anything. In order to stop dirt from dropping inside the tank, I stuck a rag in place of the cap.

Lower the tank, take your time in case it’s hanging up anywhere.

There were 4 vent lines along the top, these will be getting replaced so I cut them off. If your vehicle doesn’t have an access hole up top, then you’ll need to disconnect the fuel pump while the tank is lowered.

Once that tank is out, here it is. As far as I know, this is the original tank, the car has over 280,000km so you can see the dirt has gathered on top of the tank.

Tape up any lines where dirt can risk falling inside of the tank.

Using a vacuum and a softer wire brush, clean up all the dirt from the tank.

While there still is some fuel inside, I flipped it over for a moment to determine where the leak was. The fuel wasn’t dripping out, but the area was rusted enough to let the fuel seep where you’re able to see the residue. Fuel is lighter than water, so a leak will show up much easier.

This tank has a drain which makes removing the fuel extremely easy, but unfortunately, not all tanks have this. Using a gas can, I put a rag over the filler hole to strain any dirt out the fuel.

Considering the whole tank is getting repainted, I will be removing the fuel pump. This doesn’t necessarily need to be done if you want to keep this more on a budget basis. If you are removing the pump, you may need a new gasket depending on its condition.

Some surface sanding and wire wheeling of the tank is required, this can cause heat and sparks. Fuel fumes can be explosive even if the tank doesn’t contain any fuel. An old trick is running exhaust fumes through the tank, I let the fumes run for about an hour. By the time I got around to working on this tank, it also aired out for a week. The longer it airs out, the better. In addition to this, the tank can also be washed out with soap and water. Or it can also be filled with argon which is used for mig welding when cleaning up those rusty areas.

Getting the tank ready to clean up the rust and repair the leaking area. Considering this car had a rust coating applied, it has been oil sprayed over the years but this tank also has a wax coating which could have possibly been from shipping when it was new. Using a heat gun, this will soften up the wax coating making it very easy to remove. I used a plastic scraper so it wouldn’t scrape up the existing paint, remove the wax coating.

Wax or oil may be still on the surface, use a wax and grease remover to clean up the tank. I used paper towel as it’s easily disposable.

Remove whatever is left from the vibration pads, these will be replaced once the tank has been repainted.

Then continue to clean the top side with a wax and grease remover. It’s important to have a clean base so we don’t contaminate any areas where a leak is being repaired or even for painting.

The most efficient was to remove rust in these hard to reach areas is using a media blaster. Any opening in the tank can be plugged or taped off so no dirt, rust, or blasting media falls inside.

Using blasting equipment, strip any paint and rust from the areas. It’s important that all the rust is removed and we have a bare base when applying a sealant to the tank. I’m using glass bead for a blasting media.

If you don’t have access to sanding blasting equipment, you can use a surface sander too with 80 grit sanding discs. Abrasive pads can also be used and will strip the surface down very efficiently too. While I can strip the whole tank to bare steel, it really doesn't need. The areas which have rust will be addressed and repaired accordingly.

I was also noticing other areas around the tank seam with mild rusting, so this was stripped to bare steel as well. Fuel tanks can leak in a variety of areas, from what I’ve found more common areas tend to be places where dirt or debris can pool up and hold moisture or the tank seam where the two halves are connected together.

Now sand those areas where the rust was with 220 grit sandpaper to smoothen out the surface between the metal and existing paint. I’m not aiming for a showroom restoration, but I still want it to look clean.

Use a wax and grease remover to clean up the tank again, removing any dust or contaminants on the surface.

Using an etch primer, this will help improve paint bonding and also help reduce the risk of further rusting. Try not to get too much etch primer on the existing paint as this can sometimes cause a chemical reaction. You’ll be looking at 2-3 coats. First starting with a light coat, then medium to fully wet coats for the last two.

Back to the leaking area, while it’s an awkward area to even get the sandblaster in, some light rust is remaining in the pitting. I used a gel type rust remover to neutralize whatever was remaining. This can be applied with a brush and the solution will need to soak into the surface for a desired amount of time. This can vary between products so be sure to read the product's instructions.

The product requires the area to be rinsed using water.

Dry immediately with a cloth.

And finally, I used a heat gun on the lowest setting to remove any moisture. Compressed air can also be used. Do not use an open flame on the tank.

Here I have an aircraft grade fuel tank sealant. There are various quantities available, I purchased this online from an aircraft parts supplier. It’s a class b fuel tank sealant semkit which is able to withstand exposure to jet fuel and will cure with a flexible property.

This is a two-part product, the activator is in the long tube. Ensure that the center tube is pushed to the bottom of the container, using the supplied push stick, slowly inject the activator inside the tube. Pull it back slightly and inject more activator, do this a couple more times so it’s spread throughout the tube and this will make it easier to mix.

The tube must be twisted in a clockwise direction only. If you twist it in the opposite direction, the mixer side will disconnect and this should only be done when you’re ready to remove the inner tube. As you can see the product is slowly mixed seen by the streaking inside. This must be a uniform color. There are special machines to mix these tubes, it can also be done by hand, but instead I used an old hook from a pegboard and attached that to a drill.

Remove the center tube now by turning it counterclockwise to unscrew and then pull out.

Rubber gloves are a must, you’ll most likely end up working with your hands and it’s a bit easier to spread the product.

This is going on bare metal, a primer shouldn’t be on the leaking area as the fuel may soften the primer and cause the sealant to separate. Apply the sealant to a piece of cardboard and then apply. I’m using a mixing stick for now. This product is thick and extremely sticky so it takes some patience. Work times can vary depending on which tank sealant you get. The one I purchased does have a longer work time and will take slightly longer to cure. This one takes 36hrs to fully cure.

Make sure you’re far enough past the leaking areas to provide a strong bond and this will provide an excellent seal.

This has already hardened, I left it for 48hrs. While it is rubberized, it can still be sanded to some extent to knock down the high spots and smoothen the finish. I used 220 grit to sand out the sealant, again I’m not trying to make this repair completely hidden but I also want it to look responsibly clean.

The rest of the tank will be sanded with 400 grit sandpaper to provide a bond for the new paint.

Those irregular shapes and edges are tough to get with sandpaper so I’m using 400 grit scuffing pads. These pads won’t take down orange peel, but they will get around those hard angles.

Remove any dust from the tank using compressed air.

Give the tank a wipe down using a wax and grease remover.

Over those etch primed areas, these will get a filler primer. This is needed as the etch primer can sometimes cause an issue with the final paint layer. The filler primer can help seal the surface, providing somewhat of a barrier against moisture and also smoothen out some of those rougher areas, giving a cleaner final finish. You’ll be looking at one light coat and one or two full wet coats, so a max of three coats. Wait for 5 to 10 minutes in between coats, they can vary depending on your climate.

Finally, sand down the tank again using 400 grit sandpaper and abrasive pads. This will help remove any overspray, smoothen out those newly primed areas. If you do happen to sand through the paint or primer to bare metal, apply more primer.

Blow away any sanding dust, then give the tank a final cleaning using isopropyl alcohol to remove contaminants.

As for a choice of paint, this is really based on your choice. I wouldn’t recommend using a rock guard, asphalt coating, or something which can trap moisture and possibly cause future issues. Here I have farm implement paint from a local farm equipment supplier. This can be applied through a paint gun which I’m doing or by hand using a brush or roller. This particular paint can be thinned for a gun and the mixing instructions should be on the side of the can.

Work in a well-ventilated area away from anything you don’t want overspray on, use the correct safety equipment such as a respirator and apply the paint. Some paints can also be purchased in a spray can and you can certainly go with that route too. Any area which is required will need to be taped off such as the tip of the filler neck and the gasket sealing area for the fuel pump.

I did let the one side dry and the next day painted the other side.

After it did dry, I left it for a couple of days but this will vary depending on the thickness of paint and your climate. Considering any vibration coatings or pads were removed, these will need to be replaced. It’s a cooler day today so the coating for the tank straps was easier to install. Here I have purchased a thicker polyurethane coating which is the same that is used for stone chip guards on the vehicle’s paint. This was sold in pre-cut sizes and I took the measurements off the tank as to what was required. Ensure the surface is clean, cut it to length and then install. With the cooler day, the adhesive wasn’t as sticky which makes it much easier to apply. I used a heat gun after to soften it up once it was in place.

As for the foam pads between the tank and the structure on the car, I purchased some foam which was used as a gasket between a cap and truck box. This type of foam doesn’t absorb water or moisture so there’s a minimal chance of it causing rusting. Cut it to length, it wasn’t quite the correct size so it was doubled up. I took reference photos before the tank was stripped, using my phone I was able to determine those locations.

I did install the fuel pump to prevent any dirt from dropping inside the tank when it goes back into the car. The fuel cap can be left off, but plug the hole with a clean rag. Reinstall the tank in reverse of removal. If you do have a build in drain, make sure that is tight before filling the tank. If the tank straps are in rough condition, purchase replacements. Replace any fuel lines as needed which I did. New single eared pinch clamps were installed, along with new bolts for the tank straps. Once everything is done, fill the tank with fuel and check for any leaks. The last time I did a repair such as this, I put over 50,000km on the car over a couple of years without any issues. It’s certainly a much cheaper route than purchasing a new tank or having another used rusty tank which could possibly leak in the future.

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